1. Field of the Invention
This invention relates to an automotive driving control system, and more particularly to an automotive driving control system for controlling the driving state of an automobile determined by engine speed, torque and the like to a desired state in response to depression of the accelerator pedal.
2. Description of the Prior Art
In FIG. 1a, curves E1, E2 and E3 are contour lines joining points of equal specific fuel consumption in an ordinary automobile depicted on an orthogonal coordinate system which is used to express the operating state of an automobile, the abscissa and the ordinate respectively representing the engine speed (Ne) and the engine torque (Te). In other words, in the ordinary automobile in which a transmission having set transmission ratios is used and the engine output and/or the vehicle speed are controlled by changing the opening degree of the throttle valve, it is necessary to set the engine so that the region D of minimum specific fuel consumption corresponds to an opening degree of the throttle valve slightly smaller than the full or maximum opening degree in order to obtain a large torque during, for instance, acceleration by full opening the throttle valve and at the same time actuating, for instance, an air-fuel ratio enriching device, thereby ensuring reserve torque. When controlling the driving state of an automobile provided with such an engine, it is preferred that the operating state of the automobile be caused to fall within the region D of minimum specific fuel consumption bounded by the curve E1 or near thereto. Curve A in FIG. 1a is a contour line, for the full opening degree of the throttle valve.
In Japanese Unexamined Patent Publication No. 53(1978)-134162, there is disclosed an automotive driving control system embodying a concept for improving the specific fuel consumption. In the control device, the opening degrees and the transmission ratios optimal for the purpose described above are calculated for various operating states of the automobile and mapped, and an optimal throttle valve opening degree and an optimal transmission ratio are read out from the map according to the particular amount of depression of the accelerator pedal to control the throttle valve opening degree and the transmission ratio of the transmission.
In all of the conventional driving control systems, desired engine output and vehicle speed are obtained by controlling the opening degree of the throttle valve to change the volumetric efficiency according to the amount of depression of the accelerator pedal. This control is disadvantageous in that when the opening degree of the throttle valve is small, so-called pumping loss of the engine output occurs due to negative pressure generated downstream of the throttle valve, whereby the specific fuel consumption is lowered.